The 26-year-old was released by league rivals York city at the end of last season and has now signed a two-year-contract at Abbey Stadium.
"He's very good on the ball and he gives us several options in midfield," U's boss Jimmy Quinn told the club's official website.
"He's not the biggest player but he's very, very skilful and he's very good at set plays.
"Last season we had Jon Brady taking all our corners and free kicks and we didn't really have anybody to do that, but Mark has got excellent delivery of the ball and he was too good to miss out on.
"He's a quality player and technically he's excellent, and he's sharp and bright in and around the box too so I'm hoping he'll contribute to help out the strikers this season and get a few goals for us as well as be a good supply line.
"We've got a good balance in midfield now - players that can do different things and that's the key to it. You don't want too many players of the same type so you have some variation in your play, and I think we have the players to give us that."
Source: http://www.confguide.com/newsArticle.do?id=6746